#include<stdio.h>
int main(){
	int start_hour,start_min,end_hour,end_min;
	int start,end;
	int hh,mm;
	
	scanf("%d%d",&start,&end);
	
	start_hour = start / 100;
	start_min = start % 100;
	end_hour = end / 100;
	end_min = end % 100;
	
	hh = end_hour - start_hour;
	mm = end_min - start_min;	
	if(end_min < start_min){
		mm += 60;
		hh -= 1;
		
	}

	
	
	
	if(hh < 10 && mm < 10){
		printf("0%d:0%d",hh,mm);
	}else if(hh < 10){
		printf("0%d:%d",hh,mm);
	}else if(mm < 10){
		printf("%d:0%d",hh,mm);
	}else{
		printf("%d:%d",hh,mm);
	}
	return 0;
}
